This invention relates to a scanner set-up simulation apparatus for adjusting or checking the color separation conditions of a color scanner, by simulating a printed matter on a color monitor screen on the basis of the color component signals, which are obtained by color separating a color original.
A flow of color printing work will be briefed below. A color original is scanned by a color scanner, and a color separation film is made. A proof printing plate is made from the color separation films. The proof printing plate is set to a proof printing machine, and the proof printing is performed. If the color tone of the proof is unsatisfactory, the set-ups of the color scanner is changed and the color separation process is executed again, and the proof printing is made also again. If the color tone of the printed matter is satisfactory, a press plate is made using the color separation films, and is set to a printing machine for printing.
Such a proof printing process takes much time, cost and labor. To cope with this, many types of scanner set-up simulation apparatuses with color monitors have been developed. This type of simulation apparatus electronically executes the proof printing process in the color printing work, and of course eliminates the need for the proof printing. In the simulation apparatus, a final reproduction is displayed on the color monitor screen. An operator visually checks the monitor image, and sets desirable color separation conditions.
There are some prior arts of the scanner set-up simulation apparatus, such as U.S. Pat. No. 3,972,066 disclosing the plate checking apparatus, and U.S. Pat. No. 4,240,522 disclosing the color separation condition determining apparatus. In these prior arts, the simulation apparatus is provided separately from the color scanner. Another prior art is Japanese Patent Disclosure (KOKAI) No. 49-40819. In this prior art, the simulator is assembled into the color scanner. A further prior art is Japanese Patent Disclosure (KOKAI) No. 52-125001. This prior art partially couples the color scanner with the simulator.
The above prior arts involve some common problems. Firstly, it is very difficult to couple the simulator with various types of existing color scanners. Secondly, the simulator makes use of only some part of information collected by the color scanner. The displayed image depends largely on the image information as formed by the simulation technique, and therefore its quality is unsatisfactory, with poor resemblance. Thus, the prior arts are lack of the following essential requirements for the simulation apparatus; to use less simulation information for displaying the final reproduction, in connection with ensuring a high picture quality, and to simulate not only the color but also the image at a high speed, in connection with improvement of the workability.
Generally, the color original includes much finer density data than those of the color monitor image. The image signal obtained by scanning the color original contains fine gradation density data, since the scanner has a high reading accuracy, and a high resolution. In the succeeding electronical processing of the scanned image data, e.g. in storing the image data into a memory prior to its display by the color monitor, the image data of one image are coarsely sampled and stored in the form of 512.times.512 picture elements at most, because of the limited memory capacity of the memory. Therefore, in storing the image data into the memory, the average density of the sampled image may be offset from the average density of the color original depending on the sampling points.
In the case of the simulation apparatus used coupled with a separate color scanner, for making the color separation films the color separation conditions must manually be set to the scanner. Such a manual setting operation for color separation conditions are troublesome work and leads possibly to mistaken setting of the color separation conditions.
In some simulation apparatuses of the type in which the color component signals from the scanner are directly input to the simulation unit for the simulation of the printed matter, the voltage level of the color separation signal treated in the color scanner is different from that in the simulation unit, which composes the color separation signals and visually displays the composite one on the screen of the color monitor. For example, the signal level of the color scanner is 0 to 10 V, and that of the simulation unit is 0.7 Vp-p, equal to the usual video signal. For inputting the color component signals from the color scanner into the simulation unit, a level adjust circuit must be provided for level matching the image signal level and the DC level of the scanner with those of the simulation unit.
In a specific example to level matching, a gray scale is set on the drum surface of the color scanner. The drum is manually rotated to successively find the density indication places on the gray scale. Then, these places are irradiated with a beam spot. The reading head reads in or picks up the densities at these places. The density signal derived from the reading head is input to the level adjust circuit for level adjusting. Thus, to level adjust, the drum is rotated for each density place, and the level adjustment is made at each place. The sequence of drum rotation, beam spot irradiation, and density reading must be conducted for each color component. This is troublesome and time consuming work.
To cope with this problem, there is an approach in which the color component signals to be input to the simulation unit, are also input to an oscilloscope for level adjustment. The rotating speed of the drum of the color scanner is 10 to 20 turns per second, very slow. If the color component signals are directly input to the oscilloscope, the sweep frequency of the image signal waveform is very low. This indicates that observation of the image signal waveform by the oscilloscope and the signal level adjustment based on the observation are almost impossible from a practical viewpoint.
The simulation apparatus of this type involves an additional problem that the format of the output signal from the color scanner is not uniform for different types of color scanners. The color scanner has a rotating drum and a photo-electric head. A color original is optically and two dimensionally scanned by the head. The original (film) is set onto the drum surface. The head is shifted by a predetermined pitch in the axial direction of the drum for each rotation the drum. One scanning line signal is obtained for each turn of the drum. Each scanning line obtained is sampled by the sampling pulse, and subjected to the A/D conversion, and finally stored into the memory in the simulation unit.
The number of scanning lines and the number of samplings for each scanning line are determined by the number of picture elements of the memory. If the number of picture elements of the memory is 512.times.512, the shift pitch of the head is set to the segmental length obtained when the axial length of the color separation area in the originally wound on the drum surface is equally divided by 512. The period of the sampling pulse corresponds to the segmental value obtained when the circumferential length of the color separation area of the original is equally divided into 512 segments. The aspect ratio of the color monitor frame is 3:4, not 1:1. Therefore, the ratio of width to height of the color separation area is also set to 3:4.
This is diagrammatically illustrated in FIGS. 1A to 1D. FIG. 1A shows a color separation area (a rectangular area surrounded by a broken line) of the color scanner when a rectangular original is set around the drum. In the figure, the vertical direction coincides with the circumferential direction of the drum, and the width direction coincides with the axial direction of the drum. As seen, the ratio of height to width of the color separation area is 3:4. If the image data is read out from the memory, and used for display, the color monitor displays an image of the aspect ratio 3:4, as shown in FIG. 1B.
To rotate the image 90.degree. with the inversed aspect ratio, it is enough to read out the data from memory by interchanging the row and column addresses. In this case, if all of the data in the memory are read out and displayed, the image displayed by the monitor has the aspect ratio of 4:3, as shown in FIG. 1C, and a nondisplay area appears on the screen, as indicated by slanted lines. To eliminate the nondisplay area, the image must be expanded as shown in FIG. 1D. The width of the image in FIG. 1C contains the scanning lines 512.times.(3/4).sup.2. To expand this up to 512 scanning lines, the scanning line signal must be interpolated.
As described above, in the prior simulation apparatus, to rotate the display image by 90.degree., the row and column of the address signal are interchanged when reading out the image data from the memory. To display the image on the entire screen of the color monitor whose the aspect ratio is other than 1:1, the interpolation processing for expanding the image is essential. To realize this, a complicated circuit construction and much time for interpolation processing as well are needed.
Further, the resolution of the color scanner is different from that of the color monitor. The color scanner produces the image signal at high resolution, e.g. 150 lines/inch. The resolution of the color monitor is not so high. Usually, in the color scanner, the circumferential direction (height) of the drum is the main scanning direction, while in the color monitor, the horizontal direction (width) is the main scanning direction. Since the color monitor has 512 lines for the resolution in the height direction, to read the original of 10 inches length (axial direction), 1500 scanning lines are generated. However, the resolution of the image signal to be input from the color scanner to the simulation unit is only about 50 lines per inch, approximately 1/3 of that 1500 lines.
In the conventional color scanner, even if its head shift amount is set variable, its variable range is not so much. To transfer the image signal from the color scanner to the simulation unit, the image signal information by scanning lines must be thinned out. To this end, the circuitry including a line counter is provided.
Thus, in the conventional simulation apparatus, the sampling processing must be applied for the image signal information in the simulation unit. Therefore, the circuitry including the line counter is additionally needed. Further, the color scanner reads in the unnecessary scanning lines including those to be dropped (not sampled) later. This is wasteful particularly in time.
To display the image data stored in the memory by the display device in different modes such as a normal mode and a rotation mode, the conventional device writes the data in the specific mode. In the image reproduction, it specifies again the mode as specified when it is written, and reads out the data according to the specified data. In this way, the read out mode is selected.
In the image reproduction, therefore, to display the image data in the mode as specified when the data is written, the mode of normal or rotation as specified when the data is written, is specified again, and the read out mode is selected by a read out mode selector. Thus, the read out mode selector is additionally used. The mode designation work is needed for both the data writing and data reading.